FDA: Acetaminophen doses over 325 mg might lead to liver damage

By Holly Yan, CNN

Updated 10:15 AM ET, Thu January 16, 2014

Photos: A guide to (legal) pain relief 8 photos

Acetaminophen – This compound can ease minor muscle, back, tooth and joint pain and reduce fever. Sold under brand names such as Tylenol, Liquiprin and Panadol, it works by regulating the part of your brain that controls your body's temperature and inhibits the synthesis of prostaglandin in the central nervous system. A new study has found that it could reduce pleasure as well. Too much of the drug can cause rashes, liver failure and even death. Here's a guide to some of the most commonly used pain relief medications:

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Aspirin – Aspirin is one of the cheapest and oldest manufactured painkillers on the market. German-born scientist Felix Hoffman is credited with creating and popularizing what was then known as acetylsalicylic acid in 1899 to help ease his dad's arthritis pain. Today, it is used to ease minor aches and headaches. It works by reducing the substance in the body that causes inflammation and fever. Doctors also tell some adults to take an aspirin daily to help prevent a heart attack or stroke. People with bleeding conditions like ulcers or cardiovascular troubles like asthma are often advised to take another painkiller, as it may make those conditions worse. Some Americans are also allergic to aspirin. Americans consume more than 15 billion aspirin tablets a year.

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Ibuprofen – Ibuprofen falls into the class of drugs known as NSAIDs (nonsteroidal anti-inflammatory drugs). Sold under brand names including Motrin or Advil, it's used to treat minor aches and pains and reduce fever. It may be prescribed in stronger doses. It comes in tablet form as well as in chewable tablets, liquid suspensions and concentrated liquid drops. People who take NSAIDs may have a higher heart attack or stroke risk than those who do not, according to the National Institutes of Health. The medication can also cause ulcers, bleeding or holes in the stomach and intestine for some people. The risk may be higher if you take NSAIDs for a long time, are older or in poor health, and have three or more alcoholic drinks per day.

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Marijuana – There's been a growing acceptance of marijuana as a legitimate pain reliever, although the American Medical Association last year affirmed its opposition (PDF) to its legalization. Doctors in some states may prescribe it to ease chronic pain that comes from arthritis, migraines, Crohn's disease or other ongoing pain issues where other medicines have failed. It works by blocking the pain sensations felt by peripheral nerves. The cannabinoids in marijuana bind to endocannabinoid receptors throughout the body and can reduce pain (but also give the feeling of being high). Some research shows that it can also slow cancer development and increase appetite. Twenty states and the District of Columbia allow some legal use of marijuana, mostly for medicinal purposes.

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Hydrocodone – Hydrocodone is available only in combination with other ingredients, with different products prescribed for different uses. Some products are used to relieve moderate to severe pain, while others combat a cough, according to the National Institutes of Health. An opiate (narcotic) analgesic, hydrocodone relieves pain by changing the way the brain and nervous system respond to it. It may be habit-forming, and abuse of drugs, including hydrocodone, has become a concern in recent years. The Food and Drug Administration has proposed moving hydrocodone combination pills, known as opioids, from a Schedule III to Schedule II. Patients would have to have a written prescription from a doctor -- as opposed to a prescription over the phone -- to access them, and no refills would be allowed unless patients check in with their doctors.

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Fentanyl – Fentanyl is a prescription-only pain medication often given to cancer patients. They must be at least 18 years old to take it, or at least 16 for lozenges branded as Actiq, and they should also be taking regular doses of another narcotic pain medication. Patients must also be accustomed to the effects of narcotics. Fentanyl itself is a narcotic and changes the way the brain and nervous system respond to pain, according to the National Institutes of Health. This drug comes in the form of a lozenge, a tablet under the tongue, a film and a buccal (between the gum and cheek) tablet, as well as in injectable form. It is designed for sudden episodes of pain and should not be used more than four times a day. Overdose can cause drowsiness, dizziness, confusion, breathing problems or smaller pupils.

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Morphine – Patients take morphine for moderate to severe pain. It is an opiate (narcotic) analgesic and changes the way the brain and nervous system react to pain. Forms of morphine include tablet and solution, which are taken every four hours, as needed. Controlled- or extended-release tablets and controlled- or sustained-release capsules are for patients who need around-the-clock pain relief. Morphine can also be found as a morphine sulfate injection, as added to an IV fluid that drips through a needle or catheter, or injected into a large muscle. Morphine overdose can cause serious consequences such as breathing problems, loss of consciousness, sleepiness, slow heartbeat, blurred vision, nausea and fainting, according to the National Institutes of Health. Morphine may also be habit-forming.

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Propofol – Propofol, also known as Diprivan, became infamous when pop star Michael Jackson died after overdosing on the drug while using it as a sleep aid. The drug is typically administered intravenously by medical professionals for anesthetic purposes, such as when a patient is undergoing surgery. It's not approved to treat sleep disorders, according to the Food and Drug Administration. The drug itself does not provide pain relief but renders a patient unconscious. A patient wakes up almost immediately after an infusion is stopped, experts say. Propofol lowers blood pressure and suppresses breathing, so patients' heart function and breathing need constant monitoring, according to the Harvard Health Blog. Abuse of propofol in medical circles, however, has been a concern in recent years.

Over-the-counter drugs will be addressed in a future regulatory action

You're in pain after surgery, and your doctor prescribes you Vicodin, or maybe Percocet. But when you get home, the pain hasn't subsided and you decide to pop some Extra Strength Tylenol.

Unknowingly, you may have just taken more of the drug acetaminophen than is safe.

Acetaminophen is often used in pain medications with opioids such as oxycodone (Percocet), hydrocodone (Vicodin) and codeine (Tylenol with Codeine). These are called combination drugs, and the Food and Drug Administration is asking doctors to stop prescribing those that have more than 325 mg of acetaminophen per dose.

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"Many consumers are often unaware that many products (both prescription and OTC) contain acetaminophen, making it easy to accidentally take too much," the FDA said in a statement Tuesday.

The warning does not apply to over-the-counter drugs such as Tylenol, which contains acetaminophen. The FDA said it will address over-the-counter products in another regulatory action.

In 2011, the FDA asked manufacturers to limit the amount of acetaminophen in prescription combination drugs to 325 mg per capsule or tablet by January 2014. While more than half of the manufacturers agreed, some combination drugs with higher amounts of acetaminophen remain on the market.

The federal agency says it plans to start the process of withdrawing approval of prescription combination drugs from manufacturers that have not complied.

Taking too much of this pain reliever can lead to liver failure or death.

The FDA has set the recommended maximum for adults at 4,000 milligrams per day. It's easier to reach this limit than you might think; one gel tablet of Extra Strength Tylenol, for example, contains 500 mg.

Consumers should not take more than the prescribed dose of any medication that contains acetaminophen, according to the FDA, and should avoid taking more than one acetaminophen product at a time. Drinking alcohol while taking acetaminophen also puts you at risk.

To find out if your medications contain acetaminophen, read the drug label or the list of ingredients in the patient information leaflet that came with your prescription. Look for the word "acetaminophen" or the letters "APAP," an abbreviation sometimes used for the drug. If you are still unsure, contact your doctor or pharmacist.

Acetaminophen may also cause serious skin reactions in some people. According to the FDA, the skin reactions are rare but can be deadly. These conditions can cause blisters, serious rashes, reddening of the skin and the detachment of the upper surface of the skin, the epidermis.

Anyone who develops these types of conditions after using acetaminophen should stop taking the product immediately and visit a doctor or emergency room.